London -LRB- CNN -RRB- -- UK police arrested four people Tuesday on suspicion of traveling to Syria or supporting the fighting there .

Two men , ages 29 and 18 , and a 21-year-old woman were arrested in Manchester , northwest England , on suspicion of being involved in the commission , preparation or instigation of acts of terrorism , Greater Manchester Police said .

A fourth person , a 29-year-old man , was arrested in Oxford on the same charge , a police statement said .

All four are now being questioned by counterterror officers in Manchester .

Detective Chief Superintendent Tony Mole , head of the counterterror unit , said there was no imminent threat to anyone in Manchester or Britain .

`` The operation has been running since autumn 2013 , since we first became aware of a number of individuals traveling from the northwest to the battlefields of Syria , '' he said .

Mole said even those who travel to the region with the intention of providing humanitarian aid are putting themselves in danger .

`` We know that some have already lost their lives or been detained by the regime and badly treated , '' he said .

`` There are serious concerns that anyone traveling to Syria , whether for humanitarian reasons or because of a desire to support the Syrian opposition , may be targeted by extremist groups who want to recruit them . This could have serious repercussions for the safety of the individual concerned . ''

Syria 's civil war will this month have dragged on for three painful years .

More than 100,000 people have died and more than 680,000 others have been wounded , the United Nations has said . At least 6.5 million have been internally displaced and nearly 2.5 million people have fled to other countries .

CNN 's Carol Jordan contributed to this report .

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Four people are arrested by UK police on suspicion of Syria-related terror offenses

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The three men and a woman are being questioned by counterterror officers in Manchester

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Police say a number of people have traveled to the battlefields of Syria